Work chamfering apparatus and work chamfering method

Abstract

A work chamfering apparatus includes a work holding portion. The work holding portion includes a work table and a clamper. The work table has an upper surface having two end portions each formed with holding grains projecting out of the upper surface. The two end portions of the upper surface of the work table have a static friction coefficient greater than 0.1, which is greater than that of a center portion. When chamfering, first, the work is held by the work table and a generally U-shaped member of the clamper. At this time, the two end portions of the upper surface of the work table contact a lower surface of the work, whereas lower surfaces of respective end portions of the U-shaped member contact an upper surface of the work. In this state, a rotating center of the work is between the lower surfaces, and the lower surfaces are apart generally equally from the rotating center. Next, a tool including a first grinding stone and a second grinding stone is lowered, and the first grinding stone chamfers an upper edge of the work. Then, the tool is moved off and raised, and then the second grinding stone chamfers a lower edge of the work.

1. A work chamfering method using a work holding portion including a first surface and a second surface, the first surface of the work holding portion including a portion having a static friction coefficient greater than 0.1, the method comprising:
 a first step of holding a work with the work holding portion by contacting the first surface of the work holding portion with a first main surface of the work and by contacting the second surface of the work holding portion with a second main surface of the work; and  
 a second step of chamfering the work by using a tool;  
 wherein the work holding portion is adapted to rotate the work around a center of rotation;  
 further wherein the first surface of the work holding portion contacts the first main surface of the work at at least two remote contacting locations on the first main surface, the second surface of the work holding portion contacts the second main surface of the work at at least two remote contacting locations on the second main surface;  
 further wherein the center of rotation is between the contacting locations;  
 further wherein the work is a substantially plate segment formed into a shape including a curved line, and  
 further wherein said work is a segment of a ring.  
 
   
   
     2. The method according to  claim 1 , wherein
 the portion having the static friction coefficient greater than 0.1 is formed at two end portions of the first surface of the work holding portion, and  
 the two end portions contacting the first main surface of the work in the first step.  
 
   
   
     3. The method according to  claim 1 , wherein the portions having the static friction coefficient greater than 0.1 stick into the work in the first step. 
   
   
     4. A work chamfering method using a work holding portion including a first surface and a second surface, the first surface of the work holding portion including a center portion and two end portions, each of the two end portions having a static friction coefficient greater than that of the center portion, the method comprising:
 a first step of holding a work with the work holding portion by contacting each of the two end portions of the first surface of the work holding portion with a first main surface of the work and by contacting the second surface of the work holding portion with a second main surface of the work; and  
 a second step of chamfering the work by using a tool;  
 wherein the work holding portion is adapted to rotate the work around a center of rotation;  
 further wherein the first surface of the work holding portion contacts the first main surface of the work at at least two remote contacting locations on the first main surface, the second surface of the work holding portion contacts the second main surface of the work at at least two remote contacting locations on the second main surface;  
 further wherein the center of rotation is between the contacting locations;  
 further wherein the work is a substantially plate segment formed into a shape including a curved line, and  
 wherein said work is a segment of a ring.  
 
   
   
     5. The method according to one of claims  1  or  4 , wherein the tool includes a first grinding stone and a second grinding stone, and
 the second step includes a sub-step of chamfering one edge of the work with the first grinding stone, a sub-step of moving the tool thickness-wise of the work, and a sub-step of chamfering another edge of the work with the second grinding stone.  
 
   
   
     6. The method according to  claim 1 , wherein the work is a R—Fe—B alloy containing cobalt at a rate not smaller than 0.3 wt % and not greater than 10 wt %. 
   
   
     7. The method according to  claim 1 , wherein
 the tool includes a grinding stone, and  
 the grinding stone being rotated at a speed not slower than 2000 rpm and not faster than 5000 rpm for chamfering the work in the second step.  
 
   
   
     8. The method according to  claim 1 , wherein
 the tool includes a grinding stone, and  
 the grinding stone being rotated at a circumferential speed not slower than 125.6 m/min and not faster than 314 m/min for chamfering the work in the second step.  
 
   
   
     9. A chamfering method for chamfering a rare-earth sintered magnet, comprising the steps of:
 applying a grinding stone to the magnet to perform the chamfering;  
 rotating the grinding stone at a speed not slower than 2000 rpm and not faster than 5000 rpm, and  
 controlling the relative speed of the grinding stone with respect to an outer circumferential portion of the rare-earth sintered magnet to be not slower than 0.5 mm/sec and not faster than 7.0 mm/sec.  
 
   
   
     10. A chamfering method for chamfering a rare-earth sintered magnet, comprising the steps of:
 applying a grinding stone to the magnet to perform the chamfering;  
 rotating the grinding stone at a circumferential speed not slower than 125.6 m/min and not faster than 314 m/min, and  
 controlling the relative speed of the grinding stone with respect to an outer circumferential portion of the rare-earth sintered magnet to be not slower than 0.5 mm/sec and not faster than 7.0 mm/sec.  
 
   
   
     11. The method according to  claim 9  or  10 , wherein the grinding stone includes an abrasive grain having an average diameter not smaller than 100 μm and not greater than 270 μm. 
   
   
     12. The method according to  claim 9  or  10 , further comprising the step of supplying a coolant having a surface tension not smaller than 25 mN/m and not greater than 60 mN/m to a grinding region. 
   
   
     13. The method according to  claim 9 , or  10 , wherein the rare-earth sintered magnet contains cobalt at a rate not smaller than 0.3 wt % and not greater than 10 wt %.